呼伦贝尔草原土壤固氮微生物nifH基因多样性与群落结构

nifH gene diversity and community structure of soil nitrogen-fixing bacteria in Hulunbeier grassland,Inner Mongolia

采用聚合酶链式反应-变性梯度凝胶电泳(PCR-DGGE)技术及扩增产物序列分析方法比较研究了呼伦贝尔5种草地类型(线叶菊草原、贝加尔针茅草原、羊草草原、大针茅草原、克氏针茅草原)土壤固氮微生物nifH基因多样性及群落结构特征。结果表明,不同草地类型间土壤固氮微生物群落组成差异显著,羊草草原和大针茅草原相似性较高,相似度为67%,而其他3个草地类型间相似性较低,相似度均低于60%。羊草草原土壤nifH基因多样性最高,其次是克氏针茅草原、大针茅草原和贝加尔针茅草原,线叶菊草原最低。系统发育分析结果表明,呼伦贝尔草原土壤固氮微生物大部分属于变形菌门的α-变形菌纲,分别隶属于慢生根瘤菌属、中慢生根瘤菌属、红假单胞菌属、固氮螺菌属。5种草地类型中,克氏针茅草原土壤中联合固氮菌和自生固氮菌居多,而其他4个草地类型均以共生固氮菌为优势生态类型。

Polymerase chain reaction-denaturing gradient gel electrophoresis and sequence analysis were adopted to assess the nifH gene diversity and community structure of soil nitrogen-fixing bacteria in five types of grassland（Filifolium sibiricum steppe,Stipa baicalensis steppe,Leymus chinensis steppe,S.grandis steppe,and S.kryrowi steppe）in Hulunbeier.The nifH gene diversity of nitrogen-fixing bacteria was the highest in L.chinensis steppe,followed by in S.kryrowi,S.grandis,S.baicalensis,and F.sibiricum steppes.The community composition of nitrogen-fixing bacteria differed significantly with grassland type.In L.chinensis steppe,the community composition of nitrogen-fixing bacteria had high similarity with that in S.grandis steppe,but the similarity among other three grassland types was lower than 60%.Phylogenetic analysis showed that most nitrogen-fixing bacteria were Alpha-proteobacteria of Proteobacteria,belonging to Bradyrhizobium,Mesorhizobium,Rhodopseudomonas,and Azospirillum,respectively.In the 5 grassland types,free-living nitrogen-fixing bacteria and associative nitrogen-fixer were the major ecotypes in S.kryrowi steppe,while symbiotic nitrogen-fixer was the dominant ecotype in other four grassland types.